The invention is related to conversion of kinetic energy, which is present in various flows, such as airflows, water flows, tides, etc., into electricity. This disclosure describes various embodiments of a novel energy converter that efficiently utilizes oscillations induced by different types of a flow, in order to generate electricity or other types of energy.
The flow energy of water or wind has been utilized by mankind for centuries. The kinetic energy of the flow can be converted into rotating or oscillating movements of the affected device, where energy can further be harvested by different means.
Modern wind-powered and hydro-powered generators that based on propeller, rotor, turbine or rotating airfoil became reliable and widespread energy sources and their implementations are growing due to its economical power production and environmental benefits.
Large wind turbines, which typically located off shore or at remote areas, have increasingly being installed worldwide, providing megawatts of electric power without polluting the environment. Although the turbine-based wind generators are, in general, effective in certain conditions, they have limitations resulting from typical requirements of large open spaces (consistently high-speed winds), infrastructure development and large initial capital costs.
One if the main disadvantages of turbine-based wind generators is a limited efficiency at wide range of flow velocities, specifically, low cost-effectiveness at regimes with a lower power output and lack of the efficient adjustment to flow velocity changes.
Another frequent objection to large wind turbines is that they take a lot of space and often considered to be an eyesore.
Alternatively, small wind generators can be located at urban and suburban rooftops, in yards and along roadsides. Potentially, they could minimize electricity transmission losses and the need for additional transmission lines. However, the use of small wind generators (typically less that 10 kilowatts peak power) has generally been limited. The small wind generators currently suffer from substantial drawbacks that prevent their widespread adoption. Such limitations are the cost per produced energy, low energy capture, conversion and efficiency. In addition, most small wind turbines require a proper zoning and installations. Towers might also interfere with aviation and/or being visually obtrusive. Other disadvantages include noisy operation, rotor turbulence sensitivity and possible over-speed failures.
The alternative designs for generators that utilize kinetic energy of the flow have also been suggested. Thus, some attempts have been made to overcome the drawbacks of the common turbine-based devices and address the ‘efficiency versus footprint’ problem. Propeller-free designs, capable of operating in various environments, have been reported in U.S. Patent Application #20090097981 by C. W. Gabrys, and in US Patent Application #20090169354 by K. Kelaiditis et al.
The random motion (or random displacement) can also be considered as a source of kinetic energy. Accordingly, various electro-mechanical converters, (linear generators, for examples) and electrical schemes have been proposed for conversion of a mechanical power into electricity, for example, using the vibration energy to charge batteries. For example, U.S. Pat. No. 7,498,682 by A. P. Lemieux, describes the linear generator based on electro-magnetic solenoid, while the U.S. Pat. No. 7,504,764 by Y. S. Chang et al. discloses device for harvesting power from environmentally induced vibrations using a matrix of piezo-elements.
It should be noted, that mechanical-electrical converters, either based on solenoid- or piezo-transducers, have been significantly perfected by a watch-making industry, see, for example, U.S. Pat. No. 6,041,022 by M. X. Tu et al. and U.S. Pat. No. 5,751,091 by O. Takahashi et al.,—timepiece designs by Patek Philippe and Seiko, respectively.
While such generators can provide sufficient energy for small applications, they are not optimized for efficient conversion of energy available in various flows of gases or fluids.
Similarly to vibration-based electro-mechanical converters, another approach utilizes oscillations induced by a flow of gas or fluids to generate electricity, see US Patent Application #20080297119 and #20080129254, both by S. M. Frayne. This disclosure based on exploiting a wind flow to generate energy by using an aero-elastic flutter effect induced along at least one tensioned flexible membrane (ribbon, or ‘belt’) fixed at two or more points. Either magnetic filed generator or conductor is attached to the ribbon at certain fixed points only. The respective electro-magnetic elements are disposed at fixed points on the supporting structure, which is build around the ribbon. Implementing of such flexible membranes also requires maintaining a constant tension, which arises from a natural elasticity of the membrane, changing over longer periods of time. Feedback systems (constant-force springs or membrane anchors) were proposed to be built into the generator to alter the membrane tension in response to the flow speeds detected by an auxiliary sensor. The invention also suggests using magnetic field generator and an adjustable tension device, configured to apply an adjustable tension force between the fixed ends of the “belt” accordingly to the fluid flow velocity.
Another approach disclosed in U.S. Pat. No. 7,208,845, by B. Masters et al. and also in U.S. Pat. No. 7,199,480, by M. L. Fripp, describes an elongated arm, having a vortex shedding device at one end and an electrical power generator at an opposite end of the arm, for electrical power generations in fluid transmitting pipes (tubular strings), such as oil or water pipes. In such disclosure an elastic support keeps the arm against alternating lift-forces produced by vortices that shed by the vortex shedding device. A vortex-shedding device sheds vortices in response to fluid flow across the vibrating assembly at a frequency that is substantially equal to a resonant frequency of the vibrating assembly. A generator on the opposite side of an elongated arm generates electrical power in response to vibration of the vibrating assembly.
The previous designs required incorporation of weights in forms of coils or magnets and vortex shading devices being designed to move a substantial mass with some displacements at certain frequency. This mass needs a special vibration assembly and, in some cases, a source of instability at the oscillation onset. It limits the span of possible oscillation frequencies and/or may damp down the desired oscillation frequencies for certain flow characteristics. Moreover, in all proposed generators the weight of the vibrating element restricts the allowed transducer geometry, resulting in a limited range of oscillating frequencies needed for efficient energy conversion. Accordingly, previously disclosed vibration-based power generators are not optimized to couple the available energy of the various flows into the vibration assembly, which limits the conversion efficiency.
Furthermore, all mentioned proposals for small wind/hydro generators are not always satisfactory due to the design complexities, manufacturing cost, need for a complex mounting/control structures, high maintenance cost and low efficiency in energy production at various flow velocities. In particular, the use of mentioned flexible ribbon (membrane that fixed at two or more points) is prone to insufficient power generation due to limited production of vibrations under various conditions, restriction to high flow speeds, temperature and humidity changes, requirements for real-time adjustments, etc.
Vibration-based electro-mechanical converters are facing another problem of efficient rectifying of the generated alternating current (AC). Different attempts have been made to optimize the energy extraction from the generators by improving the rectifying electrical circuit, see for example, the U.S. Pat. No. 5,801,475 by M. Kimura for a piezo-transducer, where the storage capacitor is utilized.
There is a strong demand for a new type of low-cost/low-maintenance power generators that are capable of efficient conversion of the flow kinetic energy into electricity under various conditions, such as the flow velocities, temperature/humidity variations, etc. New, commercially feasible, small foot-print, scalable solutions are needed to overcome the previous rationales that restrained the non-turbine electrical generators from earlier implementation.
It is desirable to create such improved vibration-based power generator where the total area of the (virtually weightless) generating element is fully integrated into the oscillating assembly. In the present disclosure it is suggested not to separate the oscillating and generating elements. Accordingly, the oscillating element and generating element are monolithically integrated together, to perform as a single unit, which eliminates the need for the intermediate stages, such as pivots, arms, membranes, levers, etc. By this means, the oscillation energy is concentrated right at the location of the conducting element resulting in a higher efficiency of energy conversion. In addition, it provides an efficient conversion under wider range of frequencies, i.e. flow speed range.
The invention disclosed herein does not require an attached mass to provide a desired oscillation of the vibrating element. It also does not require any rotating, friction, grinding parts or flexible membranes to prove a quiet, virtually maintenance-free, operation.
Proposed new type of the energy converters can be manufactured using MEMS technology, also enabling the “generators on a chip” concept. The small generating cells, based on the disclosure, can become the building blocks for various generators of different scales, including very small generators or large energy-harvesting panels. In the future, flexible configurations that use multiple generating cells joined into customized structures of arbitrary shape, can become indispensable power supply for any micro- and macro-environments, where the natural or artificial flow is available.